1. Field of the Invention
The present invention relates to a device for converting normal outline data representative of an image outline consisting of a plurality of mutually connected segments, into compressed outline data whose volume is smaller than that of said normal outline data. The invention relates also to a device for converting the compressed outline data into the normal outline data.
2. Discussion of the Prior Art
In the field of printing, displaying or otherwise reproducing characters such as letters and symbols and other visible representations in a matrix of dots, there is known an output device which operates according to outline data representative of outlines of the characters and other visible images (hereinafter simply referred to as "characters"). When code signals are received by the output device, corresponding sets of outline data are read out from a memory, and are converted into respective sets of dot data which indicate the presence or absence of image dots at the appropriate picture elements of the dot matrix to form the respective characters. The presence and absence of the image dots are indicated by the dot data bits corresponding to the picture elements, which bits are either "1" or "0". The dot data are prepared according to size data indicative of the size of the characters, as well as the outline data. The use of the outline data eliminates a memory device having a relatively large data storage capacity for storing a large volume of the dot data for all the characters of different sizes available for reproduction, and permits the reproduction of the characters in many different sizes and type styles, with a high degree of image resolving power.
The outline data indicated above usually consists of coordinate data representative of X and Y coordinate values of segment specifying points which determines the positions of straight lines, curves or other segments of the outlines of the characters, and segment type data indicative of the kinds of the outline segments. The segment specifying points for a straight line consist of the start and end points of the straight line, and the segment specifying points for a Bezier curve consist of the start and end points of the curve and two control points which determine a curvature of the curve.
Generally, the outline data is stored in a read-only memory (ROM) or other memory device provided in the relevant output device. In response to an input code signal representative of a given character such as a letter, the corresponding outline data set is retrieved from the memory device, to prepare the corresponding set of dot data. In this arrangement, however, the required data storage capacity of the memory device increases with an increase in the number of the characters which are available for reproduction. For instance, a printer or display capable of printing or displaying the characters according to Level 1 and Level 2 of the Japanese Industrial Standard (JIS) requires a memory device having a larger capacity for storing the outline data, than a printer or display which is capable of printing or displaying only the JIS Level 1 characters.